Cyclic AMP accumulation following addition of adenylate cyclase activators is augmented in cultured normal rat kidney (NRK) cells treated with 2-pyridine carboxylic acid. This activation is due to increases in GTP-dependent adenylate cyclase activities, measured in purified plasma membranes. Cyclic nucleotide phosphodiesterase activity is unaffected. NAD and 1-methylnicotinamide were analyzed in several clones of normal and transformed NRK cells. Intracellular levels of both metabolites did not correlate with transformation or growth rate. Benzamide and its derivatives, known inhibitors of poly (ADP-ribose) synthetase, were demonstrated to inhibit also the enzyme, nicotinamide methyltransferase.